A significant example of neoclassical architecture, the building was constructed between 1787 and 1795 by order of Luigi Onesti Braschi, nephew of Pius VI, and probably designed by the architect Cosimo Morelli as the Pope's private residence. It incorporated, on the left, the Palazzo de Taxis and, on the right, the remains of the medieval church of S. Maria in Posterla; it was also functionally connected, via the Rampa Braschi, to the north with the ancient city and to the south with the Appian Way and the new city.